This invention relates to a pattern duplicating machine and, more particularly, to improvements in pattern duplicating machines of the type in which a master sheet containing a pattern and a copy sheet wetted with an activating fluid are pressed into engagement between a pair of rolls.
This invention is an improvement of pattern transfer machines, or duplicating machines, of the type disclosed in my U.S. Pat. Nos. 3,306,194, 3,306,195 and 3,306,196. In general, these machines duplicate, as by printing, a pattern carried by a continuously moving master sheet that moves into registered face-to-face engagement with a copy sheet to receive the pattern. During operation of the machine, the active surface of the master sheet is activated with a fluid, such as alcohol, so that a wet inked pattern can be transferred to the copy sheet. In such machines, the activating fluid is carried by the copy sheet, which is moistened with the fluid at a location upstream of the contacting station. When the master sheet and copy sheet are pressed together, the pattern is activated and ink printing is transferred to the copy sheet.
In machines of this type, it has been found desirable to arrange the paths of the moving master and copy sheets in such a manner that they are maintained in contacting registration not only during transfer, but also prior to actual transfer so that the fluid on the wetted copy sheet begins activation of the pattern for a time before transfer, thus enhancing contrast and resolution of the transferred printed matter. It is also desirable to be able to rewind the master copy sheet for reloading or for rerunning the original master. To carry out this operation satisfactorily, the supply, take-up and guiding mechanisms for the master sheet must remain in proper registration with the transfer path. For perfect transfer, it is obviously also required that the master sheet and the copy sheet be perfectly relatively stationary during the transfer process.
In the pattern transfer machine disclosed in U.S. Pat. No. 3,306,196, superior guiding of the master sheet and efficient transfer of an inked pattern from the master sheet to the copy sheet is achieved by arranging the path of the master sheet so that opposite runs of the master sheet are in actual contact with each other over a portion of the travel between the supply rolls and the pair of rolls, and by running the master sheet in physical contact with the copy sheet for a short distance prior to entering the nip between the drive roll and the counter rotating pressure roll. Although this early exposure of the master pattern to the activating fluid improves the quality of the printing, additional guides and space are required and it is sometimes difficult to ensure that the unsupported contacting sheets move perfectly together during this time. In the present invention these difficulties are avoided.
Another experience with duplicating machines of this type is uneven wetting of the copy sheet, resulting in incomplete activation of the master sheet pattern and, consequently, poor contrast or blank areas of the printed matter. This occurs whenever any surface area of the copy sheet to receive printed matter is not sufficiently wetted with the transfer fluid or if incorrect wetting pressure is applied. The machine of the present invention is effective in virtually eliminating uneven application of the fluid to the copy sheet.